West Philippine Basin
West Philippine Sea}} The West Philippine Basin, also known as the West Philippine Sea Basin, is the oceanic crust located underneath the western part of the Philippine Sea. It was formed during the early Oligocene epoch. To its southwest is the Philippine Trench, and to its east is the Kyushu-Palau Ridge. The West Philippine Basin is deeper and older than the eastern basins and has crustal heat-flow values approaching that of old oceanic crust.Watanabe, T., Epp, D., Uyeda, S., Langseth, M., and Yasui, M., 1970. Heat flow in the Philippine Sea: Tectonophysics,v. 10, p. 205–22Sclater, J. G., 1972. Heat flow and elevation of the marginal basins of the western Pacific: J. Geophys. Res., v. 77, p. 5705–5719. It is roughly bisected by the Central Basin Fault zone which comprises a band of high relief running from the northwest corner to the Kyushu-Palau Ridge near 14°N. Characterized by the presence of several submarine plateaus (Benham Rise and Anami and Oki-Daito Ridges). Genesis In terms of origin, 2 models distinguished: Trapped oceanic basin Trapped basin occurs in two stages: Emplacement of an oceanic basin and Individualization/isolation of the oceanic crust from the rest of the basin. It was invoked by Uyeda and Ben-Avraham (1972); Hilde and others (1977) and Hilde and Lee (1984) and suggests West Philippine Basin as a trapped piece of the Pacific Plate. Envisioned a N-S trending transform fault (connecting two ridges, the Kula Pacific Ridge and the Philippine Ridge/Central Basin Fault as turning into a subduction (the proto-Mariana Trench) zone following a change in the Pacific Plate’s motion from NNW to WNW during the Eocene. In this model, the basin is originally a part of the Pacific Plate which was isolated during the kinematic reorganization 43 Ma. Back-arc basin evolution Formed behind a subduction zone and involves process that creates an extensional regime oriented perpendicular to the subduction zone. First proposed by Karig (1971), shows the WPB as forming by back-arc spreading behind the Oki-Daito Ridge starting the Eocene. Crustal extension within the plate took place successively in the eastern portion of the plate to form the other inter-arc basins. Supporters include: Lewis et al. (1982); Seno and Maruyama (1984), Rangin et al. (1990); Hall et al. (1995); Lee and Lawyer (1995), and Deschamps (2002); Honza and Fujioka (2004); Queano et al. (2006). Petrology and Geochemistry Site 1201D of Ocean Drilling Program Leg 195 recovered basaltic and volcaniclastic units from the West Philippine Basin that document the earliest history of the Izu–Bonin–Mariana convergent margin. The stratigraphic section recovered at Site 1201D includes 90 m of pillow basalts, representing the West Philippine Basin basement, overlain by 459 m of volcaniclastic turbidites that formed from detritus shed from the Eocene–Oligocene proto-Izu–Bonin–Mariana island arc. Basement basalts are normal mid-ocean ridge basalt (N-MORB), based on their abundances of immobile trace elements, although fluid-mobile elements are enriched, similar to back-arc basin basalts (BABB). Sr, Nd, Pb and Hf isotopic compositions of the basement basalts are similar to those of basalts from other West Philippine Basin locations, and show an overall Indian Ocean MORB signature, marked by high 208Pb/204Pb for a given 206Pb/204Pb and high 176Hf/177Hf for a given 143Nd/144Nd. Trace element and isotopic differences between the basement and overlying arc-derived volcaniclastics are best explained by the addition of subducted sediment or sediment melt, together with hydrous fluids from subducted oceanic crust, into the mantle source of the arc lavas. In contrast to tectonic models suggesting that a mantle hotspot was a source of heat for the early Izu–Bonin–Mariana arc magmatism, the geochemical data do not support an enriched, ocean island basalt (OIB)-like source for either the basement basalts or the arc volcanic sectionhttps://academic.oup.com/petrology/article/47/2/277/1415244. See also * Philippine Sea Plate References Category:Oceanic basins of the Pacific Ocean Category:Philippine Sea